The objective of this project is to study further the defect of neuromuscular transmission that can be induced in animals by immunization with purified acetylcholine receptor from the electric ray, and so to determine if this animal preparation is a model for myasthenia gravis. The physiology of neuromuscular transmission will be studied by evoked potential electromyography and intracellular recording of synaptic events. The influence of thymectomy, the administration of immunosuppressive agents, and variations in immunization technique on the neuromuscular block will be studied. Neuromuscular synaptic abnormalities in patients with myasthenia gravis will be studied by evoked potential electromyography and intracellular recording in intercostal muscle biopsies obtained incidental to thymectomy. The influence of treatment with steroids upon these abnormalities will be evaluated. The endplates of immunized animals and myasthenia patients will be compared histochemically and ultrastructurally in order to further identify similarities between the two conditions and possibly to delineate the nature of the process whereby sensitivity to the receptor leads to neuromuscular blockade.